I think he's a pretty canny lad, not to mention very skillful. He has had injuries, and I think takes the risks pretty seriously. I'm sure they'll have assessed each shot, and (without wishing to underplay what he's doing), in general the moves with the greater chance of going wrong don't get mixed up with those performed in the more exposed locations.
Following viewing this I did also find another film of his called Drop & Roll, which is quite different. He does a knee-slide in that, while the bike goes under the 'stage', and then rejoins the bike afterwards. That's at the other end of the scale - relatively low peril, but a high chance of going wrong. In fact, from the making-of film that is also available, it appears that he only nails that for the first time after about 7 hours and on take 288.